In recent years Magnetic Tunnel Junctions (MTJ) have begun finding acceptance in industrial applications as a new type of magnetoresistive sensor, using the Tunneling Magnetoresistance (TMR) Effect of magnetic multilayer materials. In this effect the magnitude and direction of a magnetic field applied to the multilayered film changes the resistance of the multilayer film. The TMR effect is larger than the AMR (Anisotropic Magnetic Resistance) effect, and it also known to have better temperature stability than the Hall Effect. As a result, TMR magnetic field sensors have the advantages of higher sensitivity, lower power consumption, better linearity, wider dynamic range, better temperature characteristics, and lower noise than AMR, GMR, or Hall devices. Moreover, MTJs can be easily fabricated with existing chip manufacturing technology which facilitates the production of very small integrated magnetic field sensors.
Multi-axis magnetic field sensors generally have more than a single sensor chip integrated in the package, in order to provide vector measurement capability with good orthogonality. Because the magnetic field is a vector field, a multi-axis magnetic field sensor has a very wide range of applications, especially for electronic compass, which use biaxial or triaxial sensors for geomagnetic field measurements. As a result of this common application, simplified means of production of highly-integrated single-chip multi-axis magnetic field sensors are strongly desired.
When deposited on the same wafer, GMR and MTJ materials used for the different sensor axes have the same magnetic moments, and after annealing have the same pinned layer direction, which makes fabrication of single-chip three-axis sensors difficult. As such, the most common approach to manufacture a GMR triaxial sensor is to package an X-axis sensor, a Y-axis sensor, and a Z-axis sensor deposited on three different substrates; such a GMR triaxial sensor suffers limitations such as excessive size, high packaging cost, and it has a lower sensitivity and higher power consumption than a MTJ sensor.
As can be seen from the above, current AMR, Hall, and GMR triaxial sensors are disadvantageous in that they have excessive size, high packaging cost, lower sensitivity, higher power consumption, and the manufacturing methods are impractical.